The importance of adhesives in the modern world is well known, both on an industrial and professional level. They are used in a multitude of manufacturing processes to perform bonds, for example, in sectors such as graphic arts, transformation of paper and cardboard, containers and packaging, furniture and wood, the car industry, etc. They are also very important in the installation or bonding of materials, especially in construction (adhesives for pavements and coverings such as carpets, PVC, linoleum, . . . ). Even on a domestic or children's level, their use is fairly widespread. Obviously due to this great variety of fields of application, their composition is quite variable. In this way, we can have adhesives of solid, liquid, acrylic types, cyanoacrylates, epoxy, etc.
On a technical level, an adhesive is defined as a mixture of substances that serves to keep two supports bonded together by surface interactions. These interactions may be of physical or chemical type (chemical bonds). The bonding mechanism of an adhesive is based on a balance of two forces:
Adhesive force (Fa): the force that must be exerted to separate the adhesive from the surface.
Cohesive force (Fc): the force that must be exerted to break the internal structure of the adhesive.
A good adhesive is characterized in that it causes ruptures of cohesive type, i.e. the adhesive must break before separating from the support. In some cases it may be of interest that ruptures of the support appear (for structural adhesives).
A cohesive rupture is characterized as it appears in a system wherein Fc<Fa.
This can be achieved by adhesives with low Fc: low resistance bonds or by systems providing very high Fa (incorporating adherence promoters, for example).
However, one of the current difficulties is finding adhesives capable of curing when the place where they are applied is in contact with high humidity or directly in contact with water and that, furthermore, said curing is performed in the shortest possible period of time. This is of great importance when the working conditions are usually surrounded by an aqueous medium, such as, for example, in a boat, in the repair of submerged pipes, applications in plumbing, nautical construction and repairs, or, in general, any utensil which, due to its characteristics, must be in continuous contact with water and it is required that the adhesive acts as fast as possible.
Currently, there are adhesive compositions that are used for curing in said aqueous conditions but their efficacy is far from optimum. Examples of said commercial products are the Marine Adhesive fast cure 5200™ from 3 M™, or Hysol U-05FL™ from Loctite™.
Document JP2000336333 discloses a water-resistant adhesive comprising two components A and B, where component A is an epoxy resin composition modified with urethane, bisphenol A resin and acrylic particles and component B is a polyamidoamine.
Document JPS6023467 relates to an adhesive with excellent water resistance properties and is composed of formaldehyde, bisphenol A-type epoxy resin and optionally an epoxy resin hardener such as, for example, compounds with amino groups.
Document JPS59191713 discloses the use of an epoxy resin mixture derived from bisphenol A and polyamidoamine in a composition with iron oxide and a fibrous material to obtain a material with great adhesiveness to metals, wood and good resistance in water.
The present inventors have surprisingly obtained an adhesive composition with the capacity of curing, in addition to under dry conditions, under humid conditions or submerged in water (being this water, for example, pure water, fresh water, salt water, sea water, ocean water, contaminated water, and, in general, solutions where the major solvent is water) in a period of time of 30 min as much, with the capacity of bonding any type of material, whether in dry or humid conditions or submerged in water, and additionally having a flexible behaviour once cured which makes it especially indicated for demands where a flexible bond is required and with variability in form. All these properties are kept even at temperatures around 5° C.
None of the previously mentioned documents disclose an adhesive composition as disclosed in the present invention having at the same time all the above disclosed properties.
Consequently, a first object of the present invention is to achieve an adhesive composition which has the capacity to cure, in addition to under dry conditions, in an aqueous medium (i.e. submerged in water, considering that this water can be, for example, pure water, fresh water, salt water, sea water, ocean water, contaminated water, and, in general, solutions where the major solvent is water) or with humidity in the shortest possible time (30 min as much) and also be flexible, this last parameter being easily controllable by the modification of the adhesive composition.
Another object of the present invention is to develop a process whereby the adhesive composition described herein is obtained.
Another further object of the present invention is to provide the use of the adhesive composition of the present invention to bond any type of surface in any environmental condition, whether with water or without it.